1. Field of the Invention
The present invention relates to an image display device which can display different images toward plural viewpoints, a portable terminal device in which such the image display device is mounted, and a display panel which is mounted in such an image display device, and more specifically the present invention relates to an image display device, a portable terminal device and a display panel, all of which allow the electric power consumption to be reduced.
2. Description of the Related Art
Conventionally, various investigations have been made on a display device capable of displaying a three-dimensional image. Regarding the binocular vision, the Greek mathematician, Euclid, stated on 280 B.C. that “the binocular vision is a visual perception which a person can be obtained, simultaneously watching with his own left and right eyes two different images which are obtained by looking at a single object from different directions” (see, for example, an article by Chihiro Masuda, “Three-Dimensional Display”, Sangyo-Tosho, K. K.; hereinafter referred to as Non-patent literature 1). That is, the three-dimensional image display device is required in its function to provide two images having a parallax different from each other for the left and right eyes.
In the past, a greater number of three-dimensional image display methods were studied in order to actually realize such a function. The methods can generally be classified into those requiring using eyeglasses and those requiring not using eyeglasses. The anaglyph method using the color difference, and the polarized eyeglasses method using the polarization pertain to the method requiring using eyeglasses. Because it is substantially difficult to avoid troublesome resulting from the usage of eyeglasses, the methods requiring not using eyeglasses have been mostly studied in the recent years.
The lenticular lens method, and the parallax barrier method and the like pertain to the method without usage of eyeglasses. The lenticular lens method was invented on 1910 or so by Ives et al. The parallax barrier method was envisaged by Berthier on 1896, and actually demonstrated by Ives on 1903.
As described in the non-patent literature 1, the parallax barrier is a light shield (barrier) having a number of fine stripe-shaped openings, i.e., slits extending in the direction parallel to each other. A display panel is disposed on the rear side of the parallax barrier. In the display panel, pixels for one's own left eye and pixels for one's own right eye are repeatedly arranged in a direction perpendicular to the longitudinal direction of the slits. As a result, part of the light leaving each pixel is intercepted when it passes through the parallax barrier. More specifically, the pixels are arranged such that the light emerged from the pixels for the left eye arrives at the left eye of a viewer, but the light traveling toward the right eye is intercepted, whereas the light emerged from the pixels for the right eye arrives at the right eye but the light traveling toward the left eye is intercepted. Accordingly, the light emerged from the pixel for the left eye and the light emerged from the pixel for the right eye arrives respectively at the left and right eye, so that the viewer is able to identify a three-dimensional image.
FIG. 1 is a perspective view of a conventional dual eye type three-dimensional image display device using a parallax barrier, and FIG. 2 is a diagram showing an optical model of the three-dimensional image display device. As shown in FIGS. 1 and 2, the conventional three-dimensional image display device is equipped with a transmissive liquid crystal display panel 21, and display pixels are arranged in the form of a matrix in the transmissive liquid crystal display panel 21. Each display pixel includes a pixel 43 for the left eye and a pixel 44 for the right eye. In this case, the pixel 43 for the left eye and the pixel 44 for the right eye are delimited respectively by corresponding light shield sections 6. These light shield sections 6 serve to prevent the color mixing in an image as well as to transmit display signals to the pixels.
Moreover, a parallax barrier 7 is disposed in the front of the liquid crystal display panel 21, i.e., on the side of a viewer. A slit 7a extending in a direction is formed in the parallax barrier 7. The slit 7a is disposed for a pair of the pixel 43 for the left eye and the pixel 44 for the right eye. Moreover, a light source 10 is disposed in the rear of the liquid crystal display panel 21.
As shown in FIG. 2, the light emitted from the light source 10 passes through both the pixel 43 for the left eye and the pixel 44 for the right eye in the transmissive liquid crystal display panel 21, and then part of the light is intercepted in the case when the light passes through the slit 7a of the parallax barrier 7. Thereafter, the light proceeds to an area EL or ER. Accordingly, if the viewer places his own left eye 52 on the area EL and his own right eye 51 on the area ER, an image for the left eye is received with his own left eye 52 and an image for the right eye is received with his own right eye 51, thereby enabling a three-dimensional image to be identified by the viewer.
At the beginning of the parallax barrier method being demonstrated, a parallax barrier is interposed between the display panel and the viewer's own eyes, thereby causing the visibility to be reduced due to the eyesore. However, in the recent liquid crystal display device, the parallax barrier is disposed in the rear of the display panel and therefore the visibility is improved. Thus, intensive studies have been made, and, in fact, new products have been demonstrated (see, table 1 in “Nikkei Electronics” (hereinafter referred to as Non-patent literature 2), No. 838, pp. 26-27, issued on Jan. 6, 2003). The product described in the non-patent literature 2 is a parallax barrier method type three-dimensional image display device using a transmissive liquid crystal display panel.
On the other hand, the lenticular lens method is a three-dimensional image display method using a lenticular lens. Such a lenticular lens is a lens, which has a flat plane on one side and a plurality of hog-backed convex portions (cylindrical lenses) in a direction on the other side. The pixels for displaying an image for the right eye and pixels for displaying an image for the left eye are alternately arranged on the focal plane of the lens. Pixel sections each comprising a pixel for the right eye and a pixel for the left eye are arranged along a line extending in one direction such that the pixel sections pertain to a convex portion. Consequently, the light emerged from each pixel is deflected by the lenticular lens such that it proceeds either toward the left eye or the right eye, and therefore two images different from each other can be sensed respectively with the right and left eyes, thereby enabling a three-dimensional image to be confirmed by the viewer.
FIG. 3 is a perspective view of a conventional dual eye type three-dimensional image display device using a lenticular lens. FIG. 4 is a diagram showing the optical model of the three-dimensional image display device. As shown in FIGS. 3 and 4, the conventional three-dimensional image display device is equipped with a transmissive liquid crystal display panel 21, and display pixels are disposed in the form of a matrix in the liquid crystal display panel 21. A pixel 43 for the left eye and a pixel 44 for the right eye are disposed in each display pixel. In this case, a lenticular lens 3 is disposed on the front side of the liquid crystal display panel 21, i.e., on the side of a viewer. Cylindrical lenses 3a of hog-backed convex portions extending in one direction are formed parallel to each other in the lenticular lens 3. The cylindrical lenses 3a are disposed so as to keep the conformity to two pixels in the transmissive liquid crystal display panel 21, i.e., to a pair of the pixel 43 for the left eye and the pixel 44 for the right eye. Moreover, a light source 10 is disposed on the rear side of the liquid crystal display panel 21.
As shown in FIG. 4, the light emitted from the light source 10 passes through a pixel 43 for the left eye and a pixel 44 for the right eye in the transmissive liquid crystal display panel 21, and then deflected by the cylindrical lenses 3a toward either area EL or ER. When, therefore, a viewer places his own left eye 52 onto the area EL and his own right eye 51 onto the area ER, an image for the left eye is sensed with the left eye 52 and an image for the right eye is sensed with the right eye 51, thereby enabling a three-dimensional image to be confirmed by the viewer.
Undesirable light beams are “hidden” by the barrier in the parallax barrier method, whereas, in the lenticular lens method, the brightness on the display plane is not principally reduced in the three-dimensional display, compared with that of the two-dimensional display, because the proceeding direction of light is deflected. In view of this fact, intensive studies are now being made on the application of the lenticular lens method to portable devices and others, in which a high brightness display and reduced electric power consumption are particularly emphasized.
However, a portable terminal device, such as a cellular phone or the like, in which such a three-dimensional image display devices is mounted, are often used in very bright locations, such as the outdoors. In such a location, therefore, a sufficient enhancement of the brightness on a display plane is required to ensure sufficiently satisfactory visibility. In the case when such a three-dimensional image display device is mounted in such a portable terminal device, a battery is normally used as a power supply. However, the weight and size of the portable terminal device are strictly restricted, and therefore the capacity of the battery is also strictly restricted. Consequently, both the downsizing and weight saving of the portable terminal device, along with an increase in the brightness on the display plane, reduce the usable period of continuous operation after charged.
Besides the three-dimensional image display device, a display for simultaneously displaying plural images has been developed as an image display device using a lenticular lens (see Japanese Patent Laid-Open No. 332354/1994 (FIG. 9) referred to as Patent literature 1). This display simultaneously displays images different from one another in the direction of observation under the same conditions using the image distribution capability of a lenticular lens. This single display device can provide a plurality of viewers, positioned in different directions with respect to the display device, with images different from one another. The patent literature 1 describes that the use of this display device can reduce the required set-up space and the power rate as compared with a case of using ordinary single-image display devices by the number of images to be displayed.
On the other hand, semi-transmissive liquid crystal display devices capable of displaying in the reflection and transmission modes in a conventional two-dimensional image display device have been previously investigated (see, for example, Nikkei Microdevices Separate Sheets “flat panel display”, Nikkei BP Co. Ltd., pp. 108-113 and FIG. 13 (hereinafter referred to as Non-patent literature 3)). FIG. 5 is a plan view of a conventional semi-transmissive liquid crystal display device disclosed in the non-patent literature 3. As shown in FIG. 5, in the conventional semi-transmissive liquid crystal display device, each pixel 40 in a semi-transmissive liquid crystal display panel 22 comprises three color regions: R (red) region, G (green) region and B (blue) region. In addition, each color region can be divided into a transmissive region and reflective region. In other words, the pixel 40 can be divided into six regions: transmissive region (red) 41R; reflective region (red) 42R; transmissive region (green) 41G; reflective region (green) 42G; transmissive region (blue) 41B; and reflective region (blue) 42B.
In each reflective region, a metal film (not shown) is formed on the surface of the rear glass substrate of two glass substrates in the semi-transmissive liquid crystal display panel 22, in which case, a liquid crystal is in contact with the above-mentioned surface. The metal film reflects the exterior light. Accordingly, in the transmissive region, the light from the light source (not shown) passes through the liquid crystal layer (not shown) in the liquid crystal panel to form an image. In the reflective region, the exterior light, such as natural light, indoor illuminating light and others, passes through the liquid crystal layer, and the light thus passed through is reflected by the metal film, and again passes through the liquid crystal layer to form an image. Therefore, the exterior light can be used as part of a light source in a bright location where exterior light is flooded. As a result, the semi-transmissive liquid crystal display device provides a higher brightness on the display plane and reduces the electric power consumption necessary for activating the light source, compared with the transmissive liquid crystal display apparatus.
However, there are the following problems in the above prior arts. FIG. 6 is a perspective view of a conventional dual eye type three-dimensional image display device, using a semi-transmissive liquid crystal display panel in the lenticular lens method, and FIG. 7 is a diagram showing the optical model thereof.
In order to reduce the electric power consumption in the three-dimensional image display device, it is conceivable that the semi-transmissive liquid crystal display panel 22 shown in FIG. 5 can be used in the three-dimensional image display device of lenticular lens method shown in FIG. 3. However, there are the following problems in such a semi-transmissive three-dimensional image display device.
In the semi-transmissive liquid crystal display panel 22 shown in FIG. 5, each pixel 40 is approximately square and each pixel 40 is divided into three color regions R, G and B such that each color region becomes rectangular. When, therefore, each color region is divided into the transmissive region and reflective region, each color region is divided along a line extending in the longitudinal direction.
In the case when the semi-transmissive liquid crystal display panel 22 shown in FIG. 5 is used as a display panel for a three-dimensional image display device, a pair of a pixel 40 for displaying an image for the left eye (hereinafter, referred to as pixel 43 for the left eye) and a pixel for displaying an image for the right eye (hereinafter, referred to as pixel 44 for the right eye) is used as a basic pixel section. Thereby, the relationship between the paired pixels and the lenticular lens 3 can be represented, as shown in FIG. 6. For the sake of simplicity, no division for each color is given in FIG. 6. The transmissive region (red) 41R, transmissive region (green) 41G, and transmissive region (blue) 41B of a single pixel shown in FIG. 5, that is, the pixel 43 for the left eye are regarded as a transmissive region 410 of a pixel for the left eye, and the reflective region (red) 42R, reflective region (green) 42G and reflective region (blue) 42B of the pixel 43 for the left eye are regarded as a reflective region 420 of a pixel for the left eye, whereas the transmissive region (red) 41R, transmissive region (green) 41G and transmissive region (blue) 41B of the pixel 44 for the right eye, which pixel is a paired one as for the pixel 43 for the left eye, are regarded as a transmissive region 430 of a pixel for the right eye, and the reflective region (red) 42R, reflective region (green) 42G and reflective region (blue) 42B of the pixel 44 for the right eye are regarded as a reflective region 440 of a pixel for the right eye.
In the three-dimensional image display device, the transmissive region 410 of the pixel for the left eye, the reflective region 420 of the pixel for the left eye, the transmissive region 430 of the pixel for the right eye and the reflective region 440 of the pixel for the right eye are arranged in this order and in the array direction 12 of the cylindrical lens 3a, that is, in the direction perpendicular to the longitudinal direction 11 of the cylindrical lenses 3a, so as to provide the conformity to each cylindrical lens 3a. The structural arrangement other than the above in the three-dimensional display device is the same as those in the conventional device shown in FIG. 3.
As a result, as shown in FIG. 7, the light emitted from the light source 10 passes through the transmissive region 410 in the pixel for the left eye and the transmissive region 430 in the pixel for the right eye in the semi-transmissive liquid crystal panel 22, and then deflected by the cylindrical lenses 3a of the lenticular lens 3, and further travels to an area ETL or ETR. On the other hand, the exterior light is incident on the semi-transmissive liquid crystal panel 22, after passing through the lenticular lens 3. The exterior light passes through a liquid crystal layer in the reflective region 420 in the pixel for the left eye and a liquid crystal layer in the reflective region 440 in the pixel for the right eye, and then reflected by the metal film, so that it again passes through the liquid crystal layers. Thereafter, the exterior light is deflected by the cylindrical lenses 3a and proceeds toward area ERL or ERR. As a result, when a viewer places his own left eye 52 on the area ETL and his own right eye 51 on the area ERL, a three-dimensional image resulting from the transmitted light is viewed, and when the viewer places his own left eye 52 on the area ERL and his own right eye 51 on the area ERR, a three-dimensional image resulting from the reflected light is viewed. Accordingly, as shown in FIG. 7, the three-dimensional image display device using the semi-transmissive liquid crystal display panel provides a greatly reduced three-dimensional visible range respectively resulting from the transmitted light and the reflected light, compared with the three-dimensional image display device using the transmissive liquid crystal display panel.
The above description is given for the three-dimensional image display device using the lenticular lens. However, a similar problem takes place in the three-dimensional image display device using the parallax barrier. In the following, this problem is described. FIG. 8 is a perspective view of a conventional dual eye type three-dimensional image display device in the parallax barrier method using a semi-transmissive liquid crystal display panel, and FIG. 9 is a diagram showing the optical model thereof.
As shown in FIG. 8, in the three-dimensional image display device, a transmissive region 410 in the pixel for the left eye, reflective region 420 in the pixel for the left eye, transmissive region 430 in the pixel for the right eye and reflective region 440 in the pixel for the right eye are arranged in this order and in the array direction 12 of the slits 7a, that is, in the direction perpendicular to the longitudinal direction 11 of the slits 7a such that it is confirmed to each slit 7a of the parallax barrier 7. The structural arrangement other than the above of the three-dimensional image display device is the same as that of the conventional device shown in FIG. 1.
As a result, as shown in FIG. 9, the light emitted from the light source 10 passes through the transmissive region 410 in the pixel for the left eye and transmissive region 430 in the pixel for the right eye, and then part of the light is intercepted in the case when it passes through the slits 7a of the parallax barrier 7. Thereafter the light passed through proceeds in the area ETL or ETR. On the other hand, the exterior light is incident on the semi-transmissive liquid crystal panel 22 via the slits 7a, and then reflected in the reflective region 420 of the pixel for the left eye and the reflective region 440 of the pixel for the right eye. Thereafter, the exterior light proceeds in the areas ERL and ERR. If, therefore, a viewer places his own left eye 52 on the area ETL and his own right eye 51 on the area ETR, he can view a three-dimensional image resulting from the transmitted light. In the case when the viewer places his own left eye 52 on the area ERL and his own right eye 51 on the area ERR, he is able to view a three-dimensional image resulting from the reflected light. As described above, even in the semi-transmissive three-dimensional image display device using the parallax barrier method, there is a problem that the three-dimensional visible range in the transmissive display and reflective display is greatly reduced, compared with the transmissive three-dimensional image display device.
A similar problem generally occurs not only in the three-dimensional image display device but also the aforementioned display of simultaneously displaying plural images. In other words, a semi-transmissive image display device suffers significant narrow visible ranges for both transmissive display and reflection display as compared with a transmissive image display device.